1. Field of the Invention
The present invention relates generally to an air conditioner system having one or more indoor units connected to one outdoor unit and, in particular but not exclusively, to a control method of controlling the outlet temperature of a refrigerant heater, which heats a refrigerant during heating mode operation, to maintain a balance between refrigerant heating and refrigerant circulation.
2. Description of the Related Art
Air conditioning systems include heat pump type air conditioners, which work by using heat extracted from a low temperature side on a high temperature side, and refrigerant heating type air conditioners having a refrigerant heater.
In air conditioners having a refrigerant heater it is particularly important to balance refrigerant circulation with the amount of heat added during heating mode operation. This balance, furthermore, is easily disrupted as a result of significant change in refrigerant circulation, which can occur as a result of long refrigerant lines carrying a high refrigerant charge, variation in the number of operating units, and changes in the fan output of the indoor unit. When this balance is disrupted and the heat added exceeds the heat dissipation capacity of refrigerant circulation, the outlet temperature of the refrigerant heater rises excessively. This can lead to compressor temperature problems, lubricant deterioration, exhaust gas temperature problems, and other problems. Conversely, if refrigerant circulation exceeds the heating capacity of the heater, fluid return to the compressor can occur, resulting in a drop in compressor reliability, and a rise in the input to the compressor.
Addressing this problem, Japanese Patent Publications (unexamined) 58-19663 and 58-22851 teach an air conditioning system having a bypass line from the compressor to the refrigerant heater with a bypass valve connected to the bypass line. When the load changes during heating, the bypass valve opens to return refrigerant from a refrigerant outlet of the compressor to a refrigerant inlet of the refrigerant heater, thereby controlling refrigerant circulation to adjust the load.
However, when the bypass valve is opened to return refrigerant from the refrigerant outlet of the compressor to the refrigerant inlet of the refrigerant heater, heated refrigerant that normally flows to the indoor unit is diverted to the refrigerant heater. This causes an approximately 3% drop in heating capacity, and prevents 100% of the heating capacity of the system from being delivered indoors.
In addition, providing a bypass line and bypass valve makes production more difficult, and thus increases the manufacturing cost.